1. Field of the Invention
The present invention relates to a device for substantially reducing or preventing leakage of shielding gas in an arc welding gun, and especially a gas-metal arc welding (GMAW) gun, sometimes known as a metal inert gas (MIG) welding gun, supplied with a consumable welding electrode, a supply of shielding gas and electrical power supplied through a supply cable from a welding machine.
2. Description of the Prior Art
It is known in the art to use a welding gun which controllably feeds a consumable welding electrode in the form of a thin welding wire to a welding location. It is also known in the art to surround the welding location with a shielding gas to prevent extraction of contaminants, such as oxygen and nitrogen, from the ambient air. The shielding gas is usually an inert gas such as helium, argon or carbon dioxide and is continuously supplied during welding to form a shield or curtain around the tip of the electrode at the welding location.
The welding gun assembly comprises a welding gun nozzle mounted on the end of a gun tube, a connector assembly and a flexible cable assembly extending between the gun tube and the connector assembly for communication therebetween. The connector assembly has means associated therewith for connection to a power adapter which in turn is connected to a source of welding wire. The connector assembly also has a connection to a source of inert gas and a source of electric power for the welding operation. Electric power is also provided by way of the connector assembly for controlling the feeding of the welding wire, the inert gas and the electric power. The cable assembly includes a tubular wall portion having an electrically conductive portion, a passageway extending therethrough and means extending through the passageway in the cable assembly through which the welding wire passes as it moves from the connector assembly to the welding gun tube. The means extending through the passageway through which the welding wire passes includes a flexible liner having a first end extending to adjacent the welding gun tube and an opposite end extending into a bore formed in the connector assembly.
An undesirable condition of known MIG gun type welding systems is the leakage of shielding gas especially out the rear end thereof where the welding wire enters. When carbon dioxide is being used as the shielding gas, some leakage may be more tolerable because of the relatively low cost of this gas. However, when gases such as argon or helium are being used as the shielding gas, leakage becomes of much greater concern due to the relatively high cost of these gases.
Prior art attempts to reduce the amount of shielding gas leakage have resulted in constructions that are somewhat effective but still result in considerable loss of shielding gas. One such device includes a tubular member which is open from one end to receive a relatively non-resilient felt-like member with a hole therethrough for the welding electrode to pass through. The opposite end of the tubular member includes an inwardly extending portion through which a small central opening is formed for the welding wire to pass through. The same end of the device has a radially extending annular flange which is formed with a radially extending surface or shoulder that abuts the surface of the structure in which the member is positioned. The device is mounted with the flexible liner extending partially into the tubular member from the fully open end thereof and against the felt-like member which is downstream of where the welding electrode enters the opening formed in the inwardly extending portion. The known device is positioned extending into a bore in the connector assembly with the radial flange portion abutting the outer surface of the connector assembly. This construction reduces to some extent the leakage of the shielding gas where the welding electrode passes through the felt-like member but this savings is minimal mainly because the felt-like member is positioned downstream of where the wire electrode enters the opening formed in the inwardly extending portion, and the felt-like member being non-resilient and relatively loosely positioned in the tubular member allows some gas leakage to take place around and through the felt-like member and out the opening in the brass member through which the welding wire passes as well as between the tubular member and the connector assembly in which it is supported. Leakage can also occur because the radial flange portion may not form an effective seal between the tubular member and the connector assembly. Other devices comprising similar liner support means have also included seal devices for reducing the leakage of shielding gas from the area between the tubular member and the connector assembly. Such devices have included the use of "O" rings at the end of the liner between the tubular member and the support structure and some have included seals positioned around the outside diameter of the flexible liner to reduce the amount of shielding gas that surrounds the liner and leaks out the rear end thereof. Bear in mind also that the shielding gas in most systems, including the present system, enters near the rear of the system and traverses the length of the system to reach the welding area. Therefore, any possible leakage that can occur near the rear of the system will have a greater adverse effect because it is working against the back pressure of the system. Also the higher the pressure of the shielding gas the greater will be the leakage that occurs.